This invention relates to ignition systems for small internal combustion engines like those used on lawnmowers, snowblowers and the like. More particularly, this invention relates to inductive and microprocessor-controlled ignition systems for such engines.
Magneto inductive ignition systems are known that enable internal combustion engines to be started and run without the need for a separate power supply, such as a battery or an alternator. However, typical prior art inductive ignition systems have poor starting characteristics because the ignition timing is very advanced at engine starting speeds to enable the engine to run efficiently at running speeds. For example, the ignition timing may occur at about 36 degrees Before Top Dead Center (BTDC) at engine starting speeds of about 200 revolutions per minute (rpm). The ignition timing retards a fixed amount as the engine speed increases to an engine running speed, with the maximum advance being between about 5 to 9 degrees.
Magneto inductive ignition systems are often used on engines having recoil starters. One way to improve the starting characteristics and to minimize kick-back of the recoil starter is to physically move the inductive system by 5 degrees in the Before Top Dead Center direction. Although this placement of the inductive ignition system improves starting characteristics, it also results in an undesirable loss of horsepower due to poor timing at engine running speeds, which are typically about 3,000 to 3,600 rpm.
Electronic and microprocessor-controlled ignition systems are also known for small internal combustion engines. One advantage of a microprocessor-controlled ignition system is that ignition timing advance is not fixed as in a discrete component, electronic inductive system; the ignition timing may be advanced by any desired amount as a function of the engine's speed. A major disadvantage of microprocessor-controlled systems, however, is that they typically require a direct current power source to operate the microprocessor. The power source is usually a battery. If the battery is not fully charged, a microprocessor-based system may be unable to start the engine since the battery may not provide sufficient power to drive the microprocessor.